I've done a bit of roasting /crystal malt making.
I'd have to go check again but it comes down to how long at what temp of course.
I remember I used a website roast your own .com maybe Google them words and it'll bring up the site.
I've had a lot of success roasting my own malts before there is a link on BF forum somewhere on my trials... https://www.brewersfriend.com/forum/posts/37436/